1. Field of The Invention
The present invention relates to a band-stop type microwave filter for use in a waveguide.
2. Description of the Prior Art
An active microwave circuit such as an oscillator or amplifier tends to emit second and third harmonics in addition to the fundamental one. These harmonics may disturb other communications in addition to the fundamental itself and hence should be suppressed. To this end, a filter is provided at the input and output terminals of microwave active circuitry.
One known microwave filter is the distributed element type wherein the series inductance thereof is defined by its microwave propagation length and the capacitance determined by a metal piece disposed in the microwave path to shorten the electric field distribution distance.
However, as this conventional filter must be at least as long as one wavelength of the fundamental harmonic it suffers from the drawback of being overly long. By way of example, a filter of this type for use in the 10 GHz band is from 4 to 10 cm in length. Further, as the metal piece must be very carefully machined and installed, the device tends to be very difficult to adjust and expensive to manufacture.
Therefore, a microwave filter which is highly compact and light in weight, has long been awaited especially in the field of radar or satellite communication wherein such requirements are of extreme importance.